The extraction of lower alcohols, especially ethanol, from aqueous solutions thereof, especially very dilute solutions, in order to recover the alcohol has become increasingly important in recent years.
J. W. Roddy, Ind. Eng. Chem. Process Des. Dev., 1981, 20, 104-108 discloses the increased interest in the use of alcohol as an additive to gasoline to improve the octane rating and extend its supply. The use of ethanol, in particular, for this purpose has become increasingly important. Present methods for recovering ethanol, however, have proven expensive in connection with cost and energy consumed because of the need to recover ethanol from water by distillation. Since most ethanol containing waste streams are very dilute in ethanol concentration, distillation has proven to be too costly. It has been determined that a balance between distillation cost and the amount of ethanol recovered centers at aqueous concentrations of ethanol of about 15-25%. Roddy discusses the use of various phosphorus solvents such as triisobutyl phosphate, tris(2-methylbutyl)phosphate, tri-n-butyl phosphate, tris-2-ethylhexyl phosphate and diamyl amyl phosphonate for the extraction of ethanol from aqueous solutions thereof and, although functional, these solvents and the others related therein have not proven to be as effective as at first believed because of their undesirable water-solubility and hydrolytic instability.
U.S. Pat. No. 4,346,241 is directed to the extraction of alcohols from aqueous solutions utilizing liquid secondary amines and aromatic cyclic amines such as quinoline, 4-n-propylpyridine. These extractants, although relatively insoluble in water are not as effective extractants for ethanol as is required because of their instability at temperatures of distillation. The amines decompose into colored species during distillation and are therefore unacceptable as well as being non-recoverable under these conditions.
C. L. Munson et al, Ind. Eng. Chem. Process Des. Dev. 1984, 23, 109-115, have further investigated the factors influencing extraction of ethanol from aqueous solution however, only the extractants disclosed by prior investigation are set forth therein.
Other extractants for ethanol have also been investigated e.g. fluorocarbons (U.S. Pat. No. 4,260,826) and dibutyl phthalate, Science, Oct. 5, 1979. Halogenated hydrocarbons e.g. Freon 11 are impractical because they must be boiled off and recondensed thereby proving costly while dibutyl pthalate hydrolyzes at the distillation temperature of ethanol.
N. E. Bell of Battelle Memorial Institute, Sept. 1981, Pacific Northwest Laboratory, in a report prepared for the U.S. Dept. of Energy under Contract DE-A CO6-76 RLO 1830, available from National Technical Information Service, U.S. Department of Commerce, 5285 Port Royal Road, Springfield, Va. 22151, disclosed that tri-n-octyl phosphine oxide (TOPO) in methyl isobutylketone or kerosene at ratios of 10:90, respectively, and other solvents were used to extract biomass gasification wastewaters which were rich in acetic and propionic acids. The wastewaters also contained ethanol. Two of the solvents investigated were shown to extract ethanol, i.e. n-butanol and methylisobutyl ketone. The report is silent, however, with regard to the extraction of ethanol or any other alcohol by the TOPO based materials investigated.
It can therefore be seen that extensive experimental work is ongoing in connection with the extractors of alcohols from aqueous solution and that if most of the disadvantages of those systems presently uncovered could be overcome, a long-felt need would be satisfied.